1. Field of the Invention
The present invention relates to a rear suspension for a vehicle having a sub-frame and more particularly, to a rear independent suspension which is capable of toe-control by a front arm and the sub-frame independently when a transverse and longitudinal force with respect to the vehicle are applied to the wheel, thereby improving ride comfort and handling safety, and at the same time being variably and easily designed.
2. Description of Conventional Art
A suspension for a vehicle connects an axle shaft and a car body to each other, and controls a position of a tire with respect to the car body for its ideal position during running, of a vehicle thereby obtaining optimal handling safety, preventing the axle shaft from directly transmitting an impact or vibration from the road surface to the car body, preventing damage of baggage, and improving the ride comfort.
Accordingly, the connection of the upper and lower portions of the suspension has to be flexible for absorbing the impact from the road surface and be durable to overcome a driving force, a braking force, and a centrifugal force applied to the wheel.
Such suspensions described above can be variably classified according to the characteristics of their structures. The suspension according to the present invention relates to a link type rear suspension, which is provided with a sub-frame and a plurality of control links.
FIGS. 6A and 6B are plan views of the conventional link type suspension comprising a sub-frame mounted on a lower portion of the car body, a plurality of control links for connecting the sub-frame to a wheel supporter, so that each wheel can independently move up and down, and a strut assembly having a lower end fixed to a knuckle arm and an upper end connected to the car body.
More specifically, the sub-frame 50 is coupled to the car body (not shown) by means of coupling portions 52a and 52b formed on a front end of a projection 51 projected in a forward direction on opposing ends of the sub-frame 50.
Inner ends of center and lower links 53 and 54 which are transversely arranged with respect to the car body and spaced from each other by a predetermined distance are respectively connected to a side-rear portion of the sub-frame 50. A knuckle arm 56 is connected to outer-ends of the center and the lower links 53 and 54.
A front end of a trailing arm 57 longitudinally arranged with respect to the car body is coupled to the front end of the projection 51 of the sub-frame 50, and a rear end of the trailing arm 57 is coupled to the knuckle arm 56.
Accordingly, in case a longitudinal force caused by the driving force and the braking force of the vehicle and the transverse force caused by a turning movement of the vehicle are applied to the car body, toe control is achieved by a compliance of a rubber bushing at ends of links 53, and 54 and trailing arm 57 and an arranging state of each element 53, 54, and 57.
That is, in case a longitudinal force is applied to the wheel 55, the sub-frame 50 is designed to be applied with a pulling load F caused by the longitudinal force of the wheel, thereby pulling the front portion of the projection 51 toward the wheel as shown in FIG. 6A, and in case a transverse force is applied to the wheel, the center and rear links 53 and 54 are designed to be applied with a pushing load P toward the car body caused by the transverse force, whereby the rear portion of the projection 51 is deformed as shown in FIG. 6B.
However, in such a conventional suspension, if deformation of the sub-frame is caused by the longitudinal force, the toe change occurs at both wheels of the vehicle, thereby providing a bad effect to the straight ahead position, and if the transverse force is applied to the wheel at the turning movement and the straight ahead position, the toe change occurs in an unstable car body so that the handling safety cannot be obtained.